Exterior PVC trims are growing in popularity for specifiers.

When I think of polyvinyl chloride (PVC) trims, I can’t help but remember the 1967 movie The Graduate. Dustin Hoffman, fresh from finishing college, has a friend of his father’s tell him at his graduation party: “I only have one word for you young man. Are you listening? Plastics.” To which young Dustin replies “Just how do you mean sir?” “The future is in plastics, Benjamin.”

The uncle was a little ahead of his time, but he was right. The PVC window market has all but killed the other window products. At one time aluminum windows were the dominant product, but today PVC windows dominate the residential industry. This does not mean metal is dead by a long shot. While there will be a place for both products, we should be--pardon the pun--flexible to new ideas.


The PVC industry had a rocky start in exterior construction. The first products had little to no protection from ultraviolet (UV) light and would become yellow, brittle and deteriorate prematurely. This negative experience left a bad taste with many exterior contractors and some have never gotten over it. Well, times change and they need to re-think their position.

The mention of plastic trim accessories gives the shivers to many exterior contractors. Past problems with expansion and contractions of the product made installation quite different from what they were used to with conventional metal trim accessories. Most contractors failed to see some of the benefits that the PVC plastic trims provide. Additionally, most installers of these trims proceeded without researching if there were any nuances to installing PVC rather than metal. These plastic trims are more flexible than their metal counterparts and can be used in a variety of curved, radius or arched conditions, and we know today curves are “in.” Contractors and installers should familiarize themselves with PVC and provide it as an option to clients or, at the very least, be prepared for a successful installation when directed by an architect’s specifications. Metal trims are likely to remain the mainstay, but PVC trims deserve another look.

Consider this fact: Carpenters installing wood siding are using more and more of the PVC dimensional trims as a replacement to conventional small trim boards. This business is growing at an amazing rate.

Many contractors may remember the days when some PVC manufacturers made inferior products. Some exterior trims became brittle and cracked when exposed to UV light. Today’s PVC trims are made from the same products used to make PVC windows and are almost immune to UV rays.

These trims are holding up well in many projects around the country. Because PVC plastic is largely unaffected by salt air, plastic trims have always been a favorite where the ocean and salt air are a concern. Architects and owners designing buildings along ocean coastlines will often require PVC trims on the exterior.


Plastic trims are popular for building interiors as well. Designers like curves and PVC will adapt to just about any shape imaginable. Many designers are creating compound curves and only PVC trims seem to fit the bill as architects push the envelope with wild shapes. PVC trims fit very well into the product portfolio wall and ceiling contractors must learn to install correctly. Another benefit to PVC trims is they can handle minor dings and dents as they tend to return to their original shape. PVC trims are also very easy to paint, and there is a wide variety of shapes available.

Because PVC exterior trims expand and contract with changes in temperature, installation can be a challenge if the trim is exposed to direct sunlight. This is not a problem once the PVC is encased in cement or plaster, but can be a problem in the limited time just before plastering. This movement has been a challenge for most installers and has given the trims an unfair and bad rap. Here’s what happens: The lather installs the PVC casing or control joint trims on a cold day, just as he would the metal trims he knows and is familiar with. They look great, nice and straight, so he begins to wonder what all the fuss was about that his buddies made in the yard. Some time later (perhaps days or weeks) the temperature may be very hot, with the sun beating on the siding, causing it to expand. This may cause buckling between the connection point of the siding. The trims begin to twist and deform out of shape. The same kind of problem may occur if the siding is installed in heat, and then contracts in cold temperatures, stressing the connection points. The lather is rightly concerned and puzzled that the trims he installed perfectly are now out of shape.

The problem is due to a fundamental lack of training for the field installers. You simply cannot attach PVC trims as you would metal trims. Most installers will use fasteners about every 18 inches along the trim and even push that to 24 inches for attachment. This may not meet ASTM or the specifications, but works for conventional metal trims. Nevertheless, this may not work with PVC in areas where the temperature can swing 40 degrees in a single day.

I have found that installers in the high desert areas, which are known for wild temperature swings in only a few hours, are very negative on PVC trims. Installers in areas with more even or slower-changing temperatures are much more receptive. I have seen projects in Alaska that have PVC trims installed in exterior stucco that are performing very well. Many EIFS manufacturers will only warranty specific systems when PVC trims are used.


Because these trims are inherently flexible, making a straight line can be a challenge. String lines work well as does using a straight block as a guide until the trim is completely fastened to the structure. The fastener spacing must be closer with PVC accessories and should alternate from side to side (if possible). The spacing can vary on the level of exposure to the cold night air and warmth of the sun. The good news is that once cement encases the trim, the trim rarely moves, even in fairly extreme conditions.

Manufacturers of PVC trims should be consulted for proper attachment recommendations for their products. However, the attachment of PVC trims will certainly require closer spacing than metal trims, which can be attached 12 inches on center. PVC trims should be attached to the substrate 6 to 8 inches along the trim. The attachment can be to framing, or in some cases, to wire tied to lath. Most PVC manufacturers provide connector clips that can help hold the PVC trim and prevent it from twisting and deforming as the temperature swings.

Wall and ceiling contractors are certain to run into situations where PVC trims have been specified. It is not advisable to take it upon themselves to switch products from what the architect has clearly called for on the project. PVC and metal trim accessories each have their own unique advantages and each contractor, designer and building owner must decide for themselves which is the best product for that particular job. A wall and ceiling contractor should be familiar with both products and may provide guidance, then follow directions.